ARTHRITIS & RHEUMATISM Vol. 58, No. 1, January 2008, pp 82–87 DOI 10.1002/art.23185 © 2008, American College of Rheumatology Prevalence of Malignancy in Psoriatic Arthritis Sherry Rohekar, 1 Brian D. M. Tom, 2 Agnes Hassa, 3 Cathy T. Schentag, 3 Vernon T. Farewell, 2 and Dafna D. Gladman 4 Objective. To determine the prevalence and types of malignancy in a large cohort of patients with psoriatic arthritis (PsA), and to compare this rate with that in the general population. Methods. A cohort analysis of patients who were followed up prospectively from 1978 to 2004 at the University of Toronto Psoriatic Arthritis Clinic was performed. Patients were followed up at 6–12-month intervals according to a standard protocol, which in- cluded recording of malignancy, and tracked on a computer database. The cohort was linked with a pro- vincial database to find malignancies that may have been missed by the protocol or developed after patients were lost to followup. Data were presented and analyzed using descriptive statistics and the Cox regression model with robust estimate of variance. Rates of first malignancy in the cohort were compared with rates in the population to derive standardized incidence ratios (SIRs). Results. Of the 665 patients included, 68 (10.2%) developed a malignancy at an average age of 62.4 years. The most frequently seen malignancies were breast (20.6%), lung (13.2%), and prostate (8.8%) cancer. The SIR for all cancers was 0.98 (95% confidence interval 0.77–1.24). Overall cancer type–specific SIRs were 0.69 (95% CI 0.26–1.83) for hematologic and 0.88 (95% CI 0.46–1.69) for lung cancer. In females, the SIR for breast cancer was 1.55 (95% CI 0.92–2.62), and in males, the SIR for prostate cancer was 0.65 (95% CI 0.29–1.44). Conclusion. Overall, 10.2% of patients in the Toronto PsA cohort developed cancer. The most fre- quent cancers were breast, lung, and prostate cancer. The incidence of malignancy in the large PsA cohort did not differ from that in the general population. Psoriatic arthritis (PsA) is a chronic inflamma- tory joint disease that affects 5–42% of those with psoriasis (1). Its rheumatic manifestations range from mild enthesopathy to a mutilating polyarthritis (2–5). Historically, PsA has been thought to be a benign disease compared with other forms of inflammatory arthritis, such as rheumatoid arthritis (RA). However, recent studies have revealed the destructive nature of PsA. Studies of radiographic evaluation, both at the Psoriatic Arthritis Clinic at the University of Toronto and in a clinic in Spain, have shown erosive changes in 67% of patients (2,4). In the Toronto cohort, 20% of PsA patients had complete joint destruction or anky- losis. Clinically, 11% of this cohort had pronounced physical disability (2). The prevalence of severe disease in this study approached that of RA. Studies in Britain and Spain also support the notion that there is progres- sive joint damage in PsA over time, and that severe disease at presentation is predictive of disease progres- sion (4–7). RA and other inflammatory joint diseases have been linked to an increased prevalence of malignancy (8–11). Psoriasis is also known to predispose patients to malignancy, particularly nonmelanoma cancers of the skin (12–15). Studies have also found increased rates of lung cancer (12,15) and hematologic malignancy such as lymphoma (13,16,17) in the psoriatic population. How- ever, it is difficult to attribute the increased risk of malignancy in either inflammatory arthritis or psoriasis to disease activity alone. Traditionally, both conditions have been treated with highly cytotoxic medications. The 1 Sherry Rohekar, MD, FRCPC: University of Toronto, and Centre for Prognosis Studies in the Rheumatic Diseases, Toronto Western Hospital, Toronto, Ontario, Canada; 2 Brian D. M. Tom, PhD, Vernon T. Farewell, PhD: Institute of Public Health, Cambridge, UK; 3 Agnes Hassa, BSc, Cathy T. Schentag, MSc: Centre for Prognosis Studies in the Rheumatic Diseases, Toronto Western Hospital, To- ronto, Ontario, Canada; 4 Dafna D. Gladman, MD, FRCPC: Toronto Western Research Institute, and Centre for Prognosis Studies in the Rheumatic Diseases, Toronto Western Hospital, Toronto, Ontario, Canada. Address correspondence and reprint requests to Dafna D. Gladman, MD, FRCPC, Centre for Prognosis Studies in the Rheu- matic Diseases, Toronto Western Hospital, 1E-410B, 399 Bathurst Street, Toronto, Ontario M5T 2S8, Canada. E-mail: dafna. gladman@utoronto.ca. Submitted for publication May 18, 2007; accepted in revised form September 7, 2007. 82